1,721,033 research outputs found
Identification, quantitation and origin of sulfur compounds in grape products. An approach via hyphenated mass spectrometry techniques.
Full text linkThe contribute of the Analytical Chemistry in the study of complex matrices, as for instance foodstuff, is crucial. In particular the development of chromatographic methods allows to quantify important technological, microbiological and physiological markers. The ensemble of all these information furthers a deeper and higher knowledge.
This Ph.D. project was designed to define the tools and evaluate the contribution of an important class of molecule on wine aroma.
Grape products are really important in the cultural and dietary Italian traditions; moreover Italy is both the first producer and the first consumer around the world. Oenological products have been largely studied since the early ’70, even if the lack of biochemical and microbiological knowledge and the poor sensitivity of the analytical techniques did not allow to carry an deep study on sulfur compounds.
This project, planned to bid analytical and oenological chemistry, focussed its attention on the study of sulfur compounds.
Dealing with complex matrices, the first problem we had to face was the matrix effects. The overcoming of such issue or the attempts in reducing it, costs to chemical laboratory, wasting of time and money to prepare suitable internal standards.
In this thesis we proposed a statistical approach based on the variance component model able to handle matrix effects. The benefits obtained by this approach definitely outweigh both the slightly worse sensitivity and uncertainty.
Another topic discussed in the thesis is the definition of analytical methods to quantify sulfur compounds. This subject has been studied distinguishing sulfur compounds into two sub-groups:
o fermentative sulfur compounds: molecules produced by yeast metabolisms from amino acidic precursors.
o varietal sulfur compounds: molecules present in specific variety, as conjugated with cysteine and glutathione. The free forms, which are sensorially active, are released during fermentation by means of a specific enzymatic activity.
This further classification was kept in the development of the analytical methods because the two classes required different sensitivity as well as metabolomics study were separated.
Concerning fermentative sulfur compounds a HS-SPME/GC-MS method was optimised and validated. With this method a wide range of sulfur compounds were quantified. Such tool was applied to metabolomic studies, concerning the influence of variety, ageing, yeast strain and other technological practice on the level of 13 fermentative sulfur compounds.
The results obtained from the development of the analytical method permitted to highlight the potentiality of the HS-SPME technique in sampling volatile compounds in complex matrices. This approach allows an easier and safer lab conditions, avoiding the use of organic solvents. The metabolomic studies furnished important suggestion on the influence of important oenological variables on the level of important sulfur compounds.
The last topic discussed in this thesis concerns the study of varietal sulfur compounds. The lack of suitable analytical technique, sufficiently rapid and avoiding the use of mercuro-organic compounds stimulated our research in verifying the performance of headspace technique in extracting these analytes.
We optimised and validated HS-SPME and purge and trap methods and finally we defined a non-parametric robust approach to compare performances from different analytical methods.
Owing to the recent interest of the scientific research in trying to understand the formation and evolution of varietal sulfur compounds, we focussed our attention on their precursors.
The first step was the synthesis of the putative precursors, followed by the optimisation of LC-MS/MS methods to quantify them. It was possible to identify a new precursor by LC-MS/MS experiments.
Finally, by the isolation of the enzyme potentially responsible of the biosynthesis of the varietal thiols precursors, we gave a preliminary explanation of the formation of these glutathionylated precursors during grape ripening.
By this project it has been possible to study and apply the newest analytical techniques available and it has been possible to define statistical procedures to overcome the most common issues in studying complex matrices. Furthermore it was clarified the contribution of an important class of molecules, such as sullfur compounds, on oenological matrices.Il contributo della Chimica Analitica nello studio delle matrici complesse, quali ad esempio quelle alimentari, è cruciale. In particolare lo sviluppo di metodi cromatografici avanzati può permettere di dosare importanti marker tecnologici, microbiologici e fisiologici e quindi consentire un approfondimento delle attuali conoscenze.
Questo lavoro è stato concepito allo scopo di definire gli strumenti per valutare il contributo di un’importante classe di molecole all’aroma dei vini.
Il vino riveste un ruolo di primaria importanza nelle tradizioni culturali ed alimentari Italiane, inoltre l’Italia risulta primo produttore e primo consumatore mondiale di vino. I prodotti enologici sono stati largamente studiati fin dai primi anni ’70, anche se l’assenza di conoscenze biochimiche e microbiologiche e la mancanza di tecniche analitiche sufficientemente sensibili non ha consentito lo studio esaustivo della classe dei composti solforati.
Questa tesi, nata da esigenze legate alla chimica analitica e alla chimica enologica, ha avuto come punto centrale lo studio dei composti solforati nei vini.
Il primo problema che si è dovuto affrontare nello studio di matrici complesse come quelle enologiche è stato quello relativo agli effetti matrice. Il superamento o il contenimento di questo problema crea ogni giorno costi in termini di tempo e di preparazione di opportuni standard interni. In questa tesi si è proposto un metodo statistico basato sul modello a componente di varianza in grado di gestire questo problema. I vantaggi sono notevoli, a fronte di una incertezza leggermente maggiore e di una sensibilità di poco peggiorata.
Altro argomento trattato è stata la definizione dei metodi analitici in grado di quantificare e quindi di studiare i composti solforati. Questa materia è stata affrontata riconoscendo una prima distinzione all’interno del gruppo degli analiti indagati:
o composti solforati fermentativi: molecole derivanti dal metabolismo del lievito a partire da precursori amminoacidici
o composti solforati varietali: molecole presenti in specifiche varietà come coniugati della cisteina e del glutatione e rilasciati durante la fermentazione alcolica ad opera di specifiche attività enzimatiche.
Questa suddivisione è stata mantenuta anche nello sviluppo dei metodi analitici, in quanto sensibilità richieste e conseguenze metabolomiche erano anch’esse distinte.
Per quanto riguarda i composti solforati fermentativi, durante il dottorato di ricerca è stato ottimizzato e validato un metodo HS-SPME/GC-MS per l’analisi di un’ampia gamma di molecole tipicamente derivanti dal metabolismo del lievito. Tale approccio è poi stato la base per studi di natura più squisitamente metabolomica in cui è stato verificato come il cultivar (i.e. la varietà), l’invecchiamento, il ceppo di lievito e altre pratiche tecnologiche potessero influenze il livello e l’evoluzione degli analiti indagati.
I risultati ottenuti per quanto attiene lo sviluppo del metodo in spettrometria di massa hanno potuto confermare con la tecnica SPME con campionamento in spazio di testa sia una tecnica di elezione per l’analisi di molecole volatili. Inoltre questo approccio consente una gestione semplice ed enviromental friendly in confronto con i più obsoleti metodi di estrazione con solvente. Gli studi metabolomici hanno consentito di trarre importanti considerazioni su aspetti molto importanti nella definizione della qualità del prodotto finale. Tali risultati consentono anche una trasferibilità nei settori della ricerca applicata e dell’enologia.
Come ultima classe di analiti indagati si sono studiati i composti solforati varietali. L’assenza di metodi sensibili e sufficientemente rapidi da essere applicati per studi su un numero significativo di campioni ha spinto la nostra attenzione alla verifica delle potenzialità delle tecniche in spazio di testa nel dosare queste molecole. Si sono ottimizzati e validati metodi HS-SPME e purge and trap ed è stata definita una procedura non parametrica robusta per il confronto delle performance delle diverse procedure.
Visto il recente interesse della ricerca scientifica operante nel settore al controllo della formazione ed evoluzione di queste molecole, abbiamo focalizzato la nostra attenzione sui precursori dei composti solforati varietali.
Il primo stadio è stata la sintesi di queste molecole, seguito poi dall’ottimizzazione di metodi LC-MS/MS per il dosaggio di queste molecole. In questo contesto è stato possibile identificare per la prima volta un nuovo potenziale precursore di aroma, tramite esperimenti LC-MS/MS.
Da ultimo, attraverso l’isolamento dell’enzima responsabile della biosintesi dei precursori d’aroma è stato possibile proporre una preliminare spiegazione alla formazione di tali molecole durante la maturazione della materia prima.
In conclusione, grazie a questa tesi di dottorato, è stato possibile approfondire ed applicare alcune delle più moderne tecniche analitiche a disposizione, è stato possibile definire procedure statistiche per superare i più comuni ostacoli nello studio di matrici complesse, ed è stato possibile chiarire il contributo di una classe importante di molecole come i composti solforati nelle matrici enologiche
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The polysaccharides of winemaking: From grape to wine
Full text linkBackground: Polysaccharides are a major class of complex macromolecules present in the wine matrix. These polysaccharides can be classified as being either grape or yeast derived. The key polysaccharides identified within the wine matrix are the pectic polysaccharides: polysaccharides rich in arabinose and galactose (PRAG), rhamnogalactouronans (RG-I and RG-II) and yeast mannoproteins (MP). The transformation of grapes into wine induces significant changes in the chemical composition and profile of these polysaccharides.
Scope and approach: This review aims to summarise and discuss the prevalence of polysaccharides in wine, with a focus on their profile during the transformation from grape to wine. This study emphasises the chemical complexity of the wine matrix, highlighting the many factors influencing the profile and abundance of poly-saccharides which could in turn assist winemakers in making informed decisions.
Key findings and conclusions: Many factors during grape maturation and throughout the winemaking process have been shown to influence the profile and chemical composition of polysaccharides. Environmental factors can significantly influence the polysaccharide profile of grape berries prior to harvest. Fermentation is responsible for the largest modification in the polysaccharide profile throughout vinification. Overall, the transition of must to wine is characterised by an increase in grape derived AGPs and RG-II, as well as a dramatic and progressive increase in yeast MP, especially true for wines aged on yeast lee
The interactions of wine polysaccharides with aroma compounds, tannins, and proteins, and their importance to winemaking
Full text linkA current research interest of the wine industry is the improvement of wine quality by producing wines to meet the consumers’ demands and desires. However, this requires an understanding of the complex chemical matrix and the nature of interactions between molecular components of the wine. Wine polysaccharides are macromolecules whose presence and interactions with other wine components can lead to the modulation of technological and organoleptic wine quality attributes. Indeed, grape and yeast derived polysaccharides play a major role in modulating wine astringency through interactions with exogenous salivary protein-tannin complexes formed within the oral cavity. Polysaccharides participate in the formation of colloidal particles through their interactions with wine tannins and proteins, with crucial implications on the clarity and stability of finished wines. Additionally, polysaccharides modulate wine aroma volatility and foaming. The extent to which they influence these attributes is dependent on the concentration and physico-chemical properties of all the species involved in these interactions. Overall, the structure, size and type of the polysaccharides are key components governing the success and intensity of their interactions with other species. Therefore, to better understand the relevance of polysaccharides in wine, this review discusses the molecular interactions facilitated by these species and details their potential roles within the wine matrix
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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